In Canada, PST stands for Pacific Standard Time, the time zone for the western-most portion of the country, whereas GST stands for Goods and Services Tax and is not a time zone. GST is applicable to most goods and services in Canada and has absolutely nothing to do with time-keeping.
Canada has six time zones: Pacific Standard Time, Mountain Standard Time, Eastern Standard Time, Central Standard Time, Atlantic Standard Time and Newfoundland Standard Time. Pacific Standard Time, or PST, applies to the portion of Canada that is closest to the Pacific coast. It shares this time zone with the western United States.
GST is the national sales tax. Some regions also charge a provincial sales tax or retail sales tax in addition to the GST.